4 ms·

I'd tried to do back of the the envelope calcs for that sort of thing. Resistive heat has the property that efficiency doesn't change with temperature. So you

I'd tried to do back of the the envelope calcs for that sort of thing. Resistive heat has the property that efficiency doesn't change with temperature. So you can heat a small amount of bricks to oven temp with no loss. But heat pump efficiency is very dependent. So yeah in theory you could use a heat pump to heat a heat reservoir. Where I get stuck is detailed calcs are needed to suss out the economics. That people don't tend to do this says the economics aren't strongly in favor.

thenickdude 4y ago
Heatpump hot water is an application of this, allowing the tank of water to be heated during off-peak electricity times and act as a thermal battery.
tgsovlerkhgsel 4y ago
1 metric ton of water heated by 10 K stores roughly 10000 kcal or around 12 kWh. A rule of thumb from https://www.greenmatch.co.uk/green-energy/central-heating-capacity https://www.greenmatch.co.uk/green-energy/central-heating-ca... suggests 1 kW of heating per 10 square meters (that's likely the output that's required to maintain an adequate temperature during the n-th percentile coldest days). So on a cold day, a 50 square meter apartment would need 24*5 = 120 kWh. I'd say it's pretty impractical unfortunately. Water is already the best (practical) choice in terms of heat stored per weight, and likely also per volume, and cost.
- Gibbon1 4y ago
  Last time I tried working things out it seems like concrete exterior walls with hydronic heat and external insulation would be a partial solution. But not really a thing you can add to most existing housing stock. And not a thing in the US. Roughing it I think if you used batteries you'd need to supply maybe guessing here 80kwh during the evening and night time. With a heat pump you'd need 20kwh. That's doable. Course likely over all more efficient to let the utility handle the battery end of things. Then again maybe a masonry heater makes sense if you often have excess solar and your utility is screwing you.
  - fy20 4y ago
    I live in Northern Europe where houses are built like this, and a 160m2 (1600sqft) house is typically fitted with a 8kW-12kW heat pump (heat output, so input electricity is 3x less) - which is used for hot water too. That may sound low, but the thing is houses here are very well insulated, so when you heat the masonry walls and floors to 21c it takes a very long time for the temperature to drop - the heat pump is just maintaining the heat We live in a slightly older house (which doesn't meet current insulation standards) and last year the heat consumption was 70kWh per m2. That's for heating and hot water.

thenickdude 4y ago

Heatpump hot water is an application of this, allowing the tank of water to be heated during off-peak electricity times and act as a thermal battery.

tgsovlerkhgsel 4y ago

1 metric ton of water heated by 10 K stores roughly 10000 kcal or around 12 kWh. A rule of thumb from https://www.greenmatch.co.uk/green-energy/central-heating-capacity https://www.greenmatch.co.uk/green-energy/central-heating-ca... suggests 1 kW of heating per 10 square meters (that's likely the output that's required to maintain an adequate temperature during the n-th percentile coldest days). So on a cold day, a 50 square meter apartment would need 24*5 = 120 kWh. I'd say it's pretty impractical unfortunately. Water is already the best (practical) choice in terms of heat stored per weight, and likely also per volume, and cost.

Gibbon1 4y ago
Last time I tried working things out it seems like concrete exterior walls with hydronic heat and external insulation would be a partial solution. But not really a thing you can add to most existing housing stock. And not a thing in the US. Roughing it I think if you used batteries you'd need to supply maybe guessing here 80kwh during the evening and night time. With a heat pump you'd need 20kwh. That's doable. Course likely over all more efficient to let the utility handle the battery end of things. Then again maybe a masonry heater makes sense if you often have excess solar and your utility is screwing you.
- fy20 4y ago
  I live in Northern Europe where houses are built like this, and a 160m2 (1600sqft) house is typically fitted with a 8kW-12kW heat pump (heat output, so input electricity is 3x less) - which is used for hot water too. That may sound low, but the thing is houses here are very well insulated, so when you heat the masonry walls and floors to 21c it takes a very long time for the temperature to drop - the heat pump is just maintaining the heat We live in a slightly older house (which doesn't meet current insulation standards) and last year the heat consumption was 70kWh per m2. That's for heating and hot water.